1. Field of the Invention
The present invention relates to an ignition timing setting apparatus. More particularly, the present invention relates to an engine ignition timing setting apparatus which is capable of verifying a knocking occurrence limit precisely and setting ignition timing to an advance quantity to maintain higher engine efficiency while avoiding occurrence of knocking.
2. Description of the Background Art
There is a known gasoline engine for a transportation apparatus which is preferably operated at an optimal ignition timing at all times in order to improve fuel economy and to reduce exhaust emission. In such known engine, when a compression ratio is increased for the purpose of improving thermal efficiency, knocking occurs. In recent years, in an automotive engine, a precise ignition timing control has been performed to avoid occurrence of knocking by installing a knock sensor in each cylinder. However, since such a sensing system was expensive, the sensing system could not be widely adopted in gasoline engines for vehicles.
The Japanese patent document JP-A No. H4-60151 proposes an engine load detecting apparatus that detects a load of an engine from rotational fluctuation of a crankshaft and includes a technology that advances or delays ignition timing according to the detected load. In such engine load detecting apparatus, the magnitude of intake air volume is regarded as magnitude of an engine load. Specifically, the magnitude of the intake air volume is determined according to the rotational fluctuation of the crankshaft without using a vacuum sensor of an intake pipe or a throttle opening sensor. Accordingly, without depending on an expensive sensing system, since the ignition timing can advance up to a knocking occurrence limit depending on the load when the load decreases, it can be expected that an engine is operated at an appropriate ignition timing.
However, a load of an engine may not be proportionate to intake air volume according to a difference in an air-fuel ratio or ignition timing. Therefore, in terms of the correlation between the engine load and the intake air volume, in the load detecting apparatus disclosed in the Japanese Patent document JP-A No. H4-60151, it is difficult to verify the knocking occurrence limit precisely and further to advance the ignition timing.
Accordingly, it is one of the objects of the present invention is to provide an engine ignition timing setting apparatus capable of setting an appropriate ignition timing while avoiding a knocking range by verifying the knocking occurrence range precisely.